First you need to create a table which will contain all the month year (basically it will be equal to no of bars in your viz). Lets keep 1st day on month for each record(lets call this AS_OF_DATE). Your input table/excel will look like this

AS_OF_DATE

2017-01-01

2017-01-02

2017-01-03

.

.

.

2018-11-01

2018-12-01

Now you need to join your source table with this table on 1=1 (use calculation field for join and put 1 for both sources.)

Now you need to create 3 calculation columns for each of the date AS_OF_DATE,start_date,termination_date like below: